I would like to describe/explain the working principle of the Temperature Measurement Process with the help of the following diagram. I apologize for any inconvenience.
Figure-1: Tentative Hardware Block Diagram of Temperature Measurement System
1. Your Temperature Sensor is given symbolic name TS, and it is connected to 5V supply via a 300 ohm (as you have said in your original post) resistor. According to data sheet of this sensor, it is a NTC (Negative Temperature Coefficient) type sensor.
2. According to your post, the TS provides:
(a) 4.75V when the Temperature is 50
0F ==> A(50, 4.75)
(b) 1.70V when the Temperature is 221
0F ==> B(221, 1.70)
(c) V
DT when the Temperature is T
0F ==> C(T, V
DT)
(From where have you got these values? Have you measured these practically or got it from data sheets?)
3. The DC voltage produced by TS is designated by the symbol V
DT. Here, V stands for Voltage, D stands for DC Voltage, and T stands for T
0F temperature. This means that the TS will produce a voltage V
DT (0V to 5V) when the Engine Temperature is T
0F.
4. The DC signal of the TS is sent to the Analog-to-Digital Converter (ADC) via Channel-1 (Ch1) of the ADC.
5. Based on the data of Step-2, we can draw the following response curve of TS:
Figure-2: Response curve of Temperature Sensor
6. Let us find the Equation for the ACB Line of Fig-2. It is of the form: y = mx +c.
(50 - 221) / (4.75 - 1.70) = (50 - T) / (4.75 - V
DT)
Upon simplification, we will find:
T = 316.3114 - 56.0655*V
DTValidity Check of the above equation fo T:
With V
DT = 4.75V:
T = 316.3114 - 56.0655*4.75 = 316.3114 - 266.3111 = 50.0002
0F (OK!)
With V
DT = 1.70V:
T = 316.3114 - 56.0655*1.70 = 316.3114 - 90.3113 = 221.0000
0F (OK!)
7. The DC signal of the TS sensor is sent to the Analog-to-Converter (ADC) Module via Channel-1(Ch1). The V
DT is digitized by the ADC, and it produces an equivalent 10-bit binary value. Let us designate this binary value by the symbolic name ADCT (value of ADC when the Engine Temperature is T
0F). There is a relationship between V
DT and ADCT, and it is given by: V
DT = (5/1024)*ADCT (Let us leave the derivation pending!). Using the value of V
DT, we can re-write the Equation of T of Step-6 as follows:
T = 316.3114 - 56.0655*V
DT==> T = 316.3114 - 56.0655*(5/1024)*ADCT
The Arduino Command to read the ADC value (when the input signal is at Ch-1) is:
analogRead(A1). Now, the Equation for T becomes as:
T = 316.3114 - 56.0655*(5/1024)*analogRead(A1)
8. Finally, the Arduino Coding:
void setup()
{
Serial.begin(9600); //Serial Monitor becomes active
analogReference(DEFAULT); //Vref for ADC is 5V
}
void loop()
{
//T = 316.3114 - 56.0655*(5/1024)*analogRead(A1)
float T; //T is declared as 32-bit floating point number
T = 316.3114 - 56.0655*(5/1024)*analogRead(A1); //read TS; convert to Temp and assign to T
Serial.println(T, 2); //show Temp on Serial Monitor in degree F with 2-digit after decimal point
delay(3000); //refresh temperature at 3-sec interval.
} To show the temperature value on the 7-segment display unit of Fig-1, one may consult the documents of
this link.